Method of making a laminated tobacco foil

ABSTRACT

A tobacco foil is made from at least two plies each comprising a film of predominantly reconstituted tobacco particles. Preferably, an intermediate layer of cellulose or comminuted tobacco ribs or porous inorganic materials is provided between the films. The intermediate layer may contain one or more active substances such as tobacco extract, burn control agents, ascorbic acid, magnesium perborate, odurants or flavourants. The films are precipitated from an aqueous suspension, combined and then dehydrated by pressing and thermal drying. Precipitation is carried out on a double sheet former comprising two endless screens which are inclined to one another in the sheet-forming region.

ite tates Arledter et a1.

ten [1 1' Mar. 11, 1975 1 METHOD OF MAKINGA LAMINATED TOBACCO FOIL [75]Inventors: Hanns F. Arledter, Graz; Josef Marek, Vienna, both of Austria22 Filed: May 18, 1973 21 Appl. No.: 361,594

[30] Foreign Application Priority Data 3,015,895 1/1962 Stall 35/93,252,230 5/1966 Donev 3,654,706 4/1972 Perrella...

3,659,356 5/1972 Nelsonw. 3,802,965 4/1974 Arlcdter 162/303 PrimaryExaminer-Melvin D. Rein Attorney, Agent, or FirmKem0n, Palmer &

Estabrook [57] ABSTRACT A tobacco foil is made from at least two plieseach comprising a film of predominantly reconstituted to baccoparticles. Preferably, an intermediate layer of cellulose or comminutedtobacco ribs or porous inorganic materials is provided between thefilms. The intermediate layer may contain one or more active substancessuch as tobacco extract, burn control agents, ascorbic acid, magnesiumperborate, odurants or flavourants. The films are precipitated from anaqueous suspension, combined and then dehydrated by pressing and thermaldrying. Precipitation is carried out on a double sheet former comprisingtwo endless screens which are inclined to one another in thesheetforming region.

22 Claims, 2 Drawing Figures PMENTED HARI 1 I975 SHEET 1 [IF 2 METHOD OFMAKING A LAMINATED TOBACCO FOIL The invention relates to tobacco foil.

it has already been variously proposed to produce tobacco foil by usingthe methods which are conventional in the paper industry, in thatcomminuted tobacco particles, particularly comminuted tobacco waste suchas ribs or the like, are precipiated from an aqueous suspension onto ascreen and subsequently pressed and dried. Since the requirement ofmaking an adequately thin foil plays an important role with the knownequipment and methods, it was considered obvious that the manufacture ofthe foils according to the method almost exclusively used in the paperindustry should take place by one-sided filtering and pressing on thelongitudinal screen ofa paper-making machine. Naturally, the resultantfoil consisted ofa single layer of reconstituted tobacco particles.

As a basic departure from the procedures hitherto used in making tobaccofoils, the present invention proposes to provide a tobacco foilcomprising at least two separate films of reconstituted tobaccoparticles. The term reconstituted tobacco particles is intended to meanparticles which, having regard to the components that are essential forsmoking, substantially correspond to natural tobacco. They may beparticles derived from tobacco plants the soluble components of whichhave been more or less replaced by treatment in an aqueous solution asis necessary for the formation of the foil-- or fibres which are notderived from tobacco plants but which are enriched by soluble activematerials normally contained in tobacco plants so that they can replacethe natural tobacco particles for smoking purposes.

The feature according to the present invention, which would at firstsight appear to involve difficulties in attaining the requirementsplaced on a smokable foil, is surprisingly associated with decisiveadvantages not only with regard to the properties of the finished foilbut also in connection with its manufacture.

First of. all, the invention makes it possible to introduce into thetobacco a number of materials that could hitherto be incorporated onlypartially or not at all.

For example, it is possible to provide between two films ofreconstituted tobacco particles a cellulose layer which has beenenriched with various substances. One can consider the aromaticcomponents of a tobacco extract obtained from otherwise useless tobaccodust. The use of cellulose as a carrier material for this purpose makesit possible to exclude from the intermediate layer any undesiredcompounds such as brown pigments and other higher molecular substances.It is simply necessary to obtain a pore size for the cellulose, bysuitably selecting, swelling and drying the cellulose, so that thecellulose acts as a molecular screen which only absorbs the desiredsubstances, whereas the higher molecular substances remain at thesurface and can be readily washed off.

The cellulose contains macropores having a diameter of 100 to 250 A andmicropores with a diameter of 25 to 30 A. During swelling, 80 percent ofthe water is retained in the micropores and the remaining 20 percent inthe macropores. When the fibres are dried under normal pressure, themacropore diameter irreversibly changes to 100 A. if drying of thefibres takes place in vacuum at moderate temperatures, the pores expandto 300 A. If a fibre that has already been swollen and is charged withvarious substances is dried, then these substances are irreversiblyretained in the fibre (sees Stone, Sealand: Cellulose Chemistry andTechnology, 2, 343 i968) Accordingly, readily volatile odourants such asmenthol or other terpenoidic compounds, alkyl pyrazines, and fatty acidesters can be fixed in the cellulose. They are protected during dryingby the two outer layers and are released only during combustion.

[f the combustion improving substances such as potassium nitrate whichare usually contained in tobacco foils are introduced in theintermediate layer, the crackling which is otherwise brought about bysuch substances during burning of the tobacco is suppressed. inaddition, the concentration of the tobacco improvers in a small portionof the tobacco prevents them from reducing the quality of the tobaccothrough gradual oxidation.'

More recent tests lead one to suspect that by means of ascorbic acid onecan inhibit the formation of nitrous amine in tobacco smoke. Hitherto,however, there was no possibility of actually embodying this substance,which is sensitive to light and oxygen, in the tobacco despite thegeneral suggestion that ascorbic acid should be used as a component forcigarettes. If ascorbic acid is introduced in the intermediate layerwithin the scope of the present invention, it is protected by the twoouter layers and one obtains a tobacco giving a remarkably mild tasteduring smoking.

The incorporation of magnesium perborate in tobacco foils was hithertoalso impossible because this substance is difficult to dissolve inwater. In the intermediate layer between two films of reconstitutedtobacco particles, this substance can be readily introduced as asuspension. When using elevated tempertures and in the simultaneouspresence of water, this compound will then release oxygen to producefoaming and a looser structure for the foil.

It is of course also possible to introduce in the intermediate layerodourants or flavourants or threads improving the static properties ofthe foil, any or all of these being encapsulated in plastics pellets.

Since the intermediate layer is protected by the outer layers of thefoil, it is possible to give it a particularly loose structure, whichresults in a lower surface weight, improved combustion and a reductionin the formation of smoke condensate. For example, a foil with anintermediate layer of only tobacco ribs exhibited a reduction in smokecondensate in the order of percent when compared with a cigarette ofnatural tobacco having the same weight. The incorporation of highlyactive diatomaceous earth or like compounds similarly results inloosening of the structure of the strip tobacco and hence bettercombustion and a better filling capacity of the smoking material. Ifthese highly active adsorbents are exposed by perforating the striptobacco, the filter effect of the unburnt tobacco stump is increased.The diatomaceous earth can also be charged with synthetic or naturalaroma-producing substances.

Even without the use of an intermediate layer, the formation of atobacco foil in accordance with the invention of more than one separatelayer of reconstituted tobacco particles brings about surprisingadvantages. It may first of all be mentioned that by slight departuresin the composition of the two films it is possible to produceconsiderable partial stresses in the foil if the foil segments or filmsare intimately interconnected even before drying and then driedtogether. This results in crimping of the tobacco particles cut from thefoil, which enhances the filling capacity of the tobacco and facilitatesits felting.

Above all, however, it should be noted that with foils according to theinvention composed only of two layers of reconstituted tobacco a verymarked improvement in practically all the important properties was foundto occur, not only in comparison with natural tobacco but also whencompared with the best foils available in the trade. This improvementaffected practically all the decisive properties such as weight,resistance to drawing and the number of draws for cigarettes made fromthe foil, as well as the content of moist tar, dry tar, nicotine,benzo(a)pyrene and phenol. For this clearly evident effect there are twopossible explanations, although it is emphasized that the theoreticalinvestigations in this respect have not yet been concluded.

Firstly, it is found that foils made in the conventional manner byone-sided filtering on an elongated screen exhibit a one-sidedconcentration of very fine substances whereas the coarser fibresaccumulate on the side facing the screen. With double-layer foils thathave been tested, the films are interconnected in an oppositely directedarrangement so that the proportion of finer particles in the foilincreases from the outside towards the centre. The manner of makingfoils according to the invention may be of even greater significance,according to which the films made entirely or predominantly ofreconstituted tobacco particles are precipitated from an aqueoussuspension on the two screens of a double sheet former that is basicallyknown from the paper-making industry, are subsequently combined and thendehydrated together by thermal drying. Thus, where the presentspecification makes reference to two separate foil segments or films,this should not be understood to mean that the foil according to theinvention must be made by combining two finished films. On the contrary,although the solid particles forming the two films or foil segments areprecipitated on separate screens, it is preferred to combine them beforedrying.

Details of a preferred method according to the invention for makingfoils according to the invention, as well as a suitable apparatus forperforming this method, will not be described with reference to theaccompanying diagrammatic drawings in which:-

FIG. 1 is a diagram showing an entire foil-making apparatus, and

FIG. 2 is a side elevation of a preferred form of sheet former.

To ensure a uniform content of water-soluble substances in the endproduct, there is first of all a swelling apparatus for pretreating thestarting material. Measured quantites of comminuted tobacco waste,particularly tobacco ribs but possibly also comminuted tobacco leaves,are fed to the swelling apparatus 5 by means of a belt balance 9.Heterogeneous cellulose for increasing the solidity of the finished foilis also introduced at this position.

The particles serving to form the foil must have a certain minimum sizeso that they are not rinsed away during formation of the foil. Thus,tobacco dust is only partially useful in so far that an extract isobtainable from its soluble parts. By adding such an extact, thereduction in the content of effective substances in the tinished foilcaused by the addition of heterogeneous cellulose is compensated. It ispreferred that the heterogeneous cellulose fed to the swelling apparatus5 be already saturated with such an extract.

The principal component of the swelling apparatus 5 is a worm 7 whichconveys the material whilst it is being enriched with liquid coming froma supply conduit 6. Treating apparatus 1 provided downstream of theswelling apparatus 5 comprises a series of refiners 1]. l l, 11"Beforethe swollen tobacco stem particles are supplied to these, the quantityof liquid necessary for the wet treatment is supplied through a conduit3 and mixed in by a tubular mixer 10. If more easily grindable tobaccoportions, e.g. cut tobacco leaves (gebits) are also to be treated, theyare preferably first fed to the last refiner ll".

Downstream of the refiners there is a further tubular mixer 10 whichfacilitates the addition of the considerable quantities of liquidnecessary for forming the sheet. A subsequent nodule catcher l2separates insufficiently treated components and leads them through theconduit 13 back to the previously described portion of the cycle. Asheet former 2 disposed downstream of the nodule catcher 12 is thereally essential part of the apparatus. In the illustrated case, itcomprises two moving screens 25 between which the reconstituted tobaccofoil is formed from the deposited particles of two films. Theapplication of the films to the screens 25 takes place within a closedliquid chamber formed on the one hand by the liquid in the vesselconstituted by the screens 25 and on the other hand by the liquid in thescreen and in suction boxes 22 disposed therebelow. By reason of thewater pressure of 5 to 200 centimetres of water column existing in thesheet-forming region of the screens, the sheet former can be referred toas a hydraulic double sheet former.

Excess liquid in the formation of the foil is withdrawn by ascreen-suction dehydrator 22 and subsequently by sheet suction apparatus20 connected to a vacuum pump 15. The liquid drawn off reaches thevessel 16, as does the liquid expressed by the suction presses l4 andthe felt press 23. Preferably, Root pumps with air cooling are used forforming the vacuum and Hueber suction cylinders with suction shoes areused for dehydration by means of suction presses, so that no sealingwater is used for the suction cylinders.

The vessel 16 constitutes the only intermediate reservoir in the entirecycle. lts volume is small compared with the total volume of liquidcontained in the cycle. A dosing pump 17 delivers liquid from the vessel16 into the swelling apparatus 5 through the conduit 6. Whilst theswelling apparatus 5 could be disposed outside the cycle of the liquidmechanically separated during formation of the foil, it is importantthat the treating apparatus 1 and the sheet former 2 be fed with thisliquid. This takes place by means of the dosing pump 17' and conduit 3as well as through the dosing pump 17" and a conduit 4 that is providedwith a flow meter 19 and cooling means 18. The cooling means 18 servesto keep the cycled liquid to temperatures below 15C or 10C so as tosuppress the uncontrolled growth of fungi and bacteria. The amount ofliquid required prior to formation of the sheet for the purpose ofthinning the material can be kept small by cycling it at least six timesper minute.

For the further treatment of the mechanically dehydrated foil there arethermal driers and cutting apparatus (not shown). Screen cleaningequipment is also not illustrated. For the purpose of cleaning thescreens one can use combinaations of suction and compressed air pipesfor removing 95 percent of the juice, whereupon the solution on thescreen is diluted by a small quantity of water (30 g/m with the aid ofvaporising nozzles, and further liquid is removed from the screens withthe aid of tubular suckers so that the proportion ofjuice is reduced to0.1 percent. The screens which are now pratically free from solution arecleansed under high pressure, any solid screen deposits are freed onceduring each 2 minutes of the cycle by a minimum of fresh water which maybe cycled, and, before they return to the box of substance, are againsubjected to compressed air or tubular suckers to free them from freshwater.

The function of the apparatus illustrated in FIG. l in the formation ofthe sheet will first of all be described in general terms, followed by anumerical example.

The heterogeneous cellulose or heterogeneous fibrous substance of acrimped nature in an air-dried form is saturated with concentratedtobacco solution (e.g. dust extract) of, say, to 50 percent until anoptimum quantity of liquid has been absorbed. This not only introduceswater to the fibres but also the low molecular aroma and odourant partsof the tobacco plant. An airdried cellulose fibre contains, for example,pores of 300 A diameter and all low molecular proportions with particlesizes of less than 300 A can penetrate into the fibre with the waterduring swelling.

The raw materials of tobacco, such as ribs, leaves, stems, gebits etc.already contain up to 50 percent of water-soluble substances. Thesewater-soluble substances should, as far as is possible, be retained inthe solid particles during reconstitution of the foil. Although the dryribs etc, should be swollen before they are disintegrated so as toregulate an optimum particle size and fibre length for the formation ofthe sheet, swelling does not serve the purpose of extracting the solublesubstances as is usual with known methods. On the contrary, swelling isintended even to increase the content of soluble substances in theparticles beyond the original value that is substantially the same asthat of the insoluble solid substances of the fibres.

Swelling of the tobacco ribs (e.g., l kilogramme) and tobacco wasteprior to grinding therefore takes place in about four to five times thequantity by weight of tobacco extract solution of 25 to 50 percentconcentration during an absorption of liquid up to 150 to 250 percent,it being possible to use a separate swelling cycle (not illustrated) toadd so much enriched water as is carried away by the swollen ribs.

The swollen ribs etc., which have an increased content of solublecomponents of up to 66 percent compared with their original proportionof solids, are now ground for 3 to minutes in the concentrated tobaccoextract solution which is used in the entire cycle and which comprises,say, 20 to 30 percent dry content (200 to 300 g soluble'extracts perlitre) until the size of the solid particles and the fibre length meetthe requirements of sheet formation, the solid content of the fibres(proportion of the raw material that is insoluble in water) then being 2to 6 percent. The proportion of soluble components in the swollenparticles is still about 40 percent in this phase.

This ground suspension of fibrous substance is now diluted withthescreen water of the screen water cycle of the paper machine (whichscreen water likewise contains 200 to 300 g/l of soluble components) toa solid fibre content (insouble proportion) of 0.2 to 0.4 percent, isfed to the charge for the paper machine, and within a period of ID to 30seconds a tobacco foil sheet is formed having a sheet weight for theinsoluble foil proportions of 30 to 50 g/m. A. proportion of liquidremaining in the fleece is small, i.e. the dissolved substances arepredominantly contained in the swollen particles.

Liquid is now withdrawn in known manner from the fibre fleece in the wetpress of the paper-making machine by screens, felt, pressure and vacuumup to a dry content of 25 to 40 percent. After pressing, one obtains awet tobacco foil that may have the following composition 25 percent 40g/m" solid foil components which are insoluble in water percent 120 g/mliquid with 27% of soluble solids l60g/m wet foil.

This wet foil is subjected to thermal drying and, after vaporisation ofthe desired proportion of water, one is left with a dry tobacco foil thtmay have the following composition 44.8 percent g/m foil componentswhich are insoluble in water (atro) 39.6 percent 32.5 g/m foilcomponents (atro) which are insoluble in water 1 1.6 percent 9.5 g/mwater 100.0 percent 82.0 glm For each 82 kilogramme of finished foilonly 78 kilogrammes of water (or rather 49 percent dry content) have tobe vaporised.

It is therefore characteristic of the function of the illustratedapparatus that the concentrataion of the solution during sheet formationis so adapted with liquid extraction after sheet formation that theresulting dried tobacco foil contains the desired proportion of solublesolids.

The extraction of liquid can be kept constant by pressing before drying,leaving the desired concentration of solid substances in thesheet-forming suspension to adjust itself in the cycle as regulated bythe supply of raw material.

The apparatus operates without any loss in extractable substances. Afterabout 30 to 40 minutes of enriching the water to contain about 20percent of extract upon commencement of production, the waterextractable content of the foil is stabilised and remains constant.

It is also recommended that the 15 to 20 percent tobacco solutions areobtained prior to the continuous tobacco foil production by swelling andpressing the raw tobacco substances so that no enriching of the solutionwill be necessary during commencement of foil formation.

In a practical operating range with a proportion of weight of liquid inthe foil of 75 to 80 percent after pressing there is obtained, with aconcentration of the suspension of 20 to 25 percent, a proportion byweight of soluble substances in the tobacco foil of about 40 to 50percent, which corresponds to the natural proportion.

lf treatment of the substance is continuous, the total amount ofsubstance and liquid in the cycle can be reduced to 400 to 600 kg for adaily production of (12,000 kilogrammes) with 20,000 to 24,000 kg ofwater being evaporated, so that, theoretically, the liq-- uid in thecycle is renewed every 2 to 4 hours.

EXAMPLE 1 A reconstituted tobacco foil of 44 parts by weight Winnowaribs, 36 parts by weight of gebits tobacco waste, eight parts by weightof cellulose fibres, 2 percent diglycol, 2 percentcarboxymethylcellulose, two parts by weight of Mg citrate, 0.4 percentdeactivator and 5.6 kilogramme tobacco dust is made as follows.

The tobacco dust is extracted in a countercurrent process at 40C and a25 percent concentrate is made which is stored in a vessel.

The ribs (2.2 kg/min) and cellulose presaturated with dust'extract (0.4kg/min) are continuously charged with the aid of an automaticproportioner in a volume of 120 l to a swelling apparatus 5 which isfilled with an enriched solution of concentrate at 50C, and allows theribs and the cellulose to swell for about one hour. The swollen solutionis at this time pumped in countercurrent. The 2.6 kg ribs and celluloseabsorb about 5.2 kg/min of solution during this hour, which solution isreplenished with cycled solution by means of the dosing pump 17.

The ribs and cellulose in the swollen condition are now diluted from 65kg per minute of cycled concentrate by means of the dosing pump 17 andflow continuously to the refiners ll, 11, 11" for treating the sub- 1stance. 1.8 kg of gebits waste is also added at this stage.

After grinding of the ribs and cellulose, the suspension containingabout 2 percent of solid substance is fed to the tubular mixer 10' whichis simultaneously fed with 90 llmin of cycled concentrate with the aidof the dosing pump 17". Further, from a mixing container (not shown) oneadds with the aid of a closing pump 3 litres per minute of a solution ofconcentrate containing 0.02 kg/min deactivator, 0.1 kg/min diglycol, 0.1kg/min Mg citrate and 0.1 kg/min CMC.

The unified suspensions of substance are fed with a fibre-solid densityof 0.5 percent through the nodule catcher 12 to the charge for theformation of the sheet.

To retain the fine fibrous substances, a filter layer is first formed inthe upper screen portion of the sheet former 2, by which the finefibrous substances can then be better and more completely retained inthe second sheet-forming portion.

Dehydration of the foil to 20 to 35 percent of solid content takes placein the lower double screen portion with the aid of a felt press. 5 kgtobacco foil solids (atro) with a fibre-solid content of 2.5 kg/min(atro) are separated from the screen per minute.

The paper-making machine of 1 metre screen width should produce 66 m offoil from every 187 g/m and therefore runs with a screen speed of 66m/min.

The foil is fed to the thermal drying section at a fibre consistency of20 percent. The concentration of screen water amounts to 20 percent.

Fibrous substances 38 g/m' (atro) Soluble substances 38 g/m (atro)Proportion of Water 152 g/m Wet Foil 228 g/m The dried foil consists of38 g/m fibrous substances 43.7%

38 g/m' soluble substances 43.7%

11 g/m' water 12.6%

1.60 kg of water must be evaporated for each kg of tobacco foil that isproduced.

After moderate craping drying takes place by 5 to 15 percent at a highfrequency of 27 MHz, assisted by hot air to remove the clouds of steamand by infra-red radiation drying. High frequency drying gives a veryuniform depositing of the extracts in and on the solids withoutmigration. The loss of odourants and aroma substances is small.

The permanence of craping the finished foil increases with the additionof strengthening binders (CMC).

EXAMPLE 2 The advantages of forming tobacco foils in the mannerdescribed in Example 1 are evident from a comparative test in whichnatural tobacco and foils made in the conventional manner on elongatedscreens are compared with a foil according to the present invention. Thecigarettes that were tested were in each case without filter, had alength of mm and a diameter of 8.02 mm. In the production of the foilsor the cut tobacco use was in every case made of the same mixture of 40percent European Blend, 40 percent Virginia and 20 percent Burley. Thecigarettes wer smoked to a butt length of 23 mm in accordance with theCORESTA standard. The results are shown in the following Table.

In a further test, cigarettes selected for the same draw resistance madefrom natural tobacco or conventional foils or foils according to theinvention were found to have phenol contents in the smoke of 139 y percigarette, 62.5 7 per cigarette, 31 'y per cigarette, respectively,which again demonstrates the superiority of foils according to theinvention.

The foregoing description concerned a foil composed of two layers orfilms. How one can form a foil from several layers will now be describedwith reference to FIG. 2 in which the same reference numerals areemployed for parts which are equivalent to those illustrated in FIG. 1.The FIG. 2 embodiment differs from the double sheet form in FIG. Iparticularly by the provision of separating walls 26 which sub-dividethe space above the screens 25 so that, upon supplying differentlycomposed solutions or suspensions through the conduits 27, multi-layerfoils are deposited on the screens 25.

FIG. 2 also indicates a cycle 28 for very fine particles estabalished bythe suction box 22 through the pump P. This cycle serves to reintroduceto the suspension above the screen 25 those small particles which couldnot yet be retained by the screen in the upper sheetforming region.Reintroduction is effected preferably considerably below the liquidlevel as determinend by overflows 29, desirably in the immediatevicinity of where the two films deposited on the inclined screenportions come together, at which position the material for forming amiddle layer is also introduced through a hollow wall 30. The sheetsuckers and suction cylinders 14 are preferably so powerful that themechanical dehydration of the combined films takes place exclusively inthe region where the screens run parallel to one another.

The serpentine path followed by the tobacco foil is brought about inthat the sheet is alternately sucked or pressed towards one screen andthen released therefrom by suction or compressed air and pressed orsucked against the other screen so that the screens are kept free fromsolid particles.

We claim:

1. A method of making reconstituted tobacco foil comprising at least twoseparate films containing principally tobacco particles which comprises?providing an aqueous suspension of tobacco particles by swellingcomminuted tobacco particles or iibers, subsequently grinding same andfinally diluting same with water to form an aqueous suspensioncontaining about 0.2 to 0.4 percent insoluble solids,

forming two separate wet sheets of tobacco particles by precipitatingtobacco particles from said aqueous suspension onto foraminous webs,

combining together the resulting two wet sheets in proximate face toface relationship,

dehydrating the combined sheets by pressing, and

thermally drying the combined pressed sheets.

2. The method of claim 1 wherein said separate sheets as formed have anasymmetric distribution of particles relative to the cross-section ofthe sheets with the proportion of finer particles increasing from oneside of the sheets to the other and said sheets are interconnected in anoppositely-directed arrangement so that in the combined sheets, theproportion of finer particles increases from the outside toward theinside thereof.

3. A reconstituted tobacco foil of asymmetric crosssection prepared bythe process of claim 2.

4. The method of claim 1 wherein carboxymethylcellulose is added to saidaqueous suspension as a binder which causes stiffening of said sheetsupon thermal drying.

5. The method of claim 1 wherein the compositions of said two sheetsdiffer from one another.

6. A method according to claim 1 wherein the combined wet sheets arecreped 5 to 15 percent before the thermal drying.

7. The method of claim 1 wherein an intermediate layer is interposedbetween said two wet sheets when they are combined.

8. The method according to claim 7 wherein the intermediate layercomprises cellulose fibers.

9. The method according to claim 8 wherein the cellulose is combinedwith tobacco extract.

10. The method according to claim 7 wherein the intermediate layerincludes combustion enhancers.

11. The method according to claim 10 wherein the combustion enhancer ispotassium nitrate.

12. The method according to claim 7 wherein the intermediate layercontains about 2.5 percent ascorbic acid based on the weight of thelayer.

13. The method according to claim 7 wherein the intermediate layercontains magnesium perborate.

14. The method according to claim 7 wherein the intermediate layercontains odourants or flavourants encapsulated in plastic pellets.

15. The method according to claim 17 wherein the intermediate layercontains filaments of plastic material.

16. The method according to claim 15 wherein the filaments are ofpolyethylene.

17. The method according to claim 7 wherein the intermediate layercontains threads of an inorganic material.

18. The method according to claim 17 wherein the inorganic material isglass.

19. The method according to claim 7 wherein the apparent density of theintermediate layer is less than that of the surrounding films ofreconstituted tobacco particles.

20. The method according to claim 19 wherein the intermediate layerconsists predominantly of comminuted tobacco ribs or crushed cellulose.

21. The method according to claim 19 wherein the intermediate layerconsists predominantly of porous inorganic materials.

22. The method according to claim 21 wherein the intermediate layercomprises diatomaceous earth.

1. A METHOD OF MAKING RECONSTITUTED TOBACCO FOIL COMPRISING AT LEAST TWOSEPARATE FILMS CONTAINING PRINCIPALLY TOBACCO PARTICLES WHICH COMPRISES:PROVIDING AN AQUEOUS SUSPENSION OF TOBACCO PARTICLES BY SWELLINGCOMMINUTED TOBACCO PARTICLES OR FIBERS, SUBSEQUENTLY GRINDING SAME ANDFINALLY DILUTING SAME WITH WATER TO FORM AN AQUEOUS SUSPENSIONCONTAINING ABOUT 0.2 TO 0.4 PERCENT INSOLUBLE SOLIDS, FORMING TWOSEPARATE WET SHEETS OF TOBACCO PARTICLES BY PRECIPITATING TOBACCOPARTICLES FROM SAID AQUEOUS SUSPENSION ONTO FORAMINOUS WEBS, COMBININGTOGETHER THE RESULTING TWO WET SHEETS IN PROXIMATE FACE TO FACERELATIONSHIP, DEHYDRATING THE COMBINED SHEETS BY PRESSING, AND THERMALLYDRYING THE COMBINED PRESSED SHEETS.
 1. A method of making reconstitutedtobacco foil comprising at least two separate films containingprincipally tobacco particles which comprises: providing an aqueoussuspension of tobacco particles by swelling comminuted tobacco particlesor fibers, subsequently grinding same and finally diluting same withwater to form an aqueous suspension containing about 0.2 to 0.4 percentinsoluble solids, forming two separate wet sheets of tobacco particlesby precipitating tobacco particles from said aqueous suspension ontoforaminous webs, combining together the resulting two wet sheets inproximate face to face relationship, dehydrating the combined sheets bypressing, and thermally drying the combined pressed sheets.
 2. Themethod of claim 1 wherein said separate sheets as formed have anasymmetric distribution of particles relative to the cross-section ofthe sheets with the proportion of finer particles increasing from oneside of the sheets to the other and said sheets are interconnected in anoppositely-directed arrangement so that in the combined sheets, theproportion of finer particles increases from the outside toward theinside thereof.
 3. A reconstituted tobacco foil of asymmetriccross-section prepared by the process of claim
 2. 4. The method of claim1 wherein carboxymethylcellulose is added to said aqueous suspension asa binder which causes stiffening of said sheets upon thermal drying. 5.The method of claim 1 wherein the compositions of said two sheets differfrom one another.
 6. A method according to claim 1 wherein the combinedwet sheets are creped 5 to 15 percent before the thermal drying.
 7. Themethod of claim 1 wherein an intermediate layer is interposed betweensaid two wet sheets when they are combined.
 8. The method according toclaim 7 wherein the intermediate layer comprises cellulose fibers. 9.The method according to claim 8 wherein the cellulose is combined withtobacco eXtract.
 10. The method according to claim 7 wherein theintermediate layer includes combustion enhancers.
 11. The methodaccording to claim 10 wherein the combustion enhancer is potassiumnitrate.
 12. The method according to claim 7 wherein the intermediatelayer contains about 2.5 percent ascorbic acid based on the weight ofthe layer.
 13. The method according to claim 7 wherein the intermediatelayer contains magnesium perborate.
 14. The method according to claim 7wherein the intermediate layer contains odourants or flavourantsencapsulated in plastic pellets.
 15. The method according to claim 7wherein the intermediate layer contains filaments of plastic material.16. The method according to claim 15 wherein the filaments are ofpolyethylene.
 17. The method according to claim 7 wherein theintermediate layer contains threads of an inorganic material.
 18. Themethod according to claim 17 wherein the inorganic material is glass.19. The method according to claim 7 wherein the apparent density of theintermediate layer is less than that of the surrounding films ofreconstituted tobacco particles.
 20. The method according to claim 19wherein the intermediate layer consists predominantly of comminutedtobacco ribs or crushed cellulose.
 21. The method according to claim 19wherein the intermediate layer consists predominantly of porousinorganic materials.